This invention relates generally to optical devices and, more particularly, to systems and methods for filtering bright light sources for use with optical devices.
Vision is affected by the amount of light illuminating the various objects in our view. By flipping a switch, for example, the contents of a dark room become immediately ascertainable. Eyes are thus light-processing organs.
The human eye includes several features for processing light. Muscles in the iris allow the pupil to open and close, regulating the amount of light received by the retina. Receptors on the surface of the retina become desensitized in response to bright-light ambients. The eyelids may “squint” the eye, for more effective viewing of a scene.
Other optical devices emulate the human eye. Photographic cameras, for example, typically include a diaphragm comprising a circular hole through which light may pass. Like the iris, the diaphragm adjusts the size of the hole, as needed, to regulate the amount of light received onto the film of the camera. A shutter blocks light, similar to the eyelids. Video cameras, binoculars and other optical devices may include similar features.
Where very bright light sources interrupt a view of a scene, the eyelids may naturally react by squinting. However, the viewable scene in such circumstances may be severely impaired. In some situations, such as operating a motor vehicle at sunrise or sunset, avoiding lasers fired by enemy aircraft, or taking off or landing an airplane, such visual impairment may even be dangerous.
Traditionally, bright sources may be compensated for by using a filtration system. A filter may be added to the optical device to impede some of light from reaching the eye or receptor. Sunglasses and helmet visors, for example, may include ultraviolet (UV) filters to prevent part of the visible light spectrum from reaching the eye. Filters may also be added to cameras, for use in bright light environments. Filtration systems, however, may block not just the bright source, but other light sources in the scene, affecting the visibility of remaining images. In conditions of high contrast, that is, where bright light is contrasted by a dark environment, the surrounding dark environment may be quite difficult or even impossible to perceive using the filtration system.
Alternatively, a bright light source may be blocked entirely from view. Automobile visors may be used for this purpose. Such blocking systems typically impair the view of other objects. For example, in response to a very bright light source, such as a loser beam, the variable iris of a camera may close entirely. The receptor of the camera may be protected from damage, but, during this time, the receptor is also blinded.
Many of the prior art solutions require the receptor to stay in one position, are slow to respond to a bright light source, or block more than the bright source, impeding view of the remaining scene. Thus, there is a continuing need for a dynamic filtration device that may more effectively block bright light sources, yet allow a clear visual image to be received.